Subject AIS 700. ( new april 2018 ) with AC antenna of 2,8 m high above the boat
My AIS 700 has always worked perfectly, now suddenly I can only receive stations at a distance of +/- 1 nm where it used to be up to +/- 15 nm. The transmission of my position appears to work well and the VHF connected to the same antenna also works well, when I connect the AIS 700 to my PC via ProAIS2 the antenna appears to be OK, but I see that there are only about twenty signals inside come from stations up to +/- 1 nm, where it used to be much more stations up to +/- 15 nm
What can be the problem

Please check the VSWR in the PRO AIS2 diagnostics, ideally it should be about 1.5:1, if it is higher, then check the antenna cable connections, a poor connection can dramatically reduce the range of the transmission.

Try an alternative antenna if possible to check if there are any issues, bear in mind whilst the antenna may work fine with vhf, it may not by efficient with the AIS700 and so if there are deteriorating connections in the cable to the antenna, then this will impact the range.

OK i see the VSWR, 1.6:1 should be OK, have you tried an alternative antenna?

Are the targets static or moving? The fact that PRO AIS2 also shows the same range in the AIS700 direct would suggest that if all else checks out Ok, the there is likely an issue with the AIS700 itself. Can you get a local dealer to check the antenna with a VSWR meter to double check what PRO AIS is reporting?